Conventional gas turbine engines utilizing a can-annular combustion arrangement include a transition duct that receives hot combustion gases from a combustor can and guides the combustion gases toward a turbine inlet. Typically a guide vane between the downstream end of the transition duct and the turbine rotor inlet orients the hot gases for delivery onto the first row of turbine blades. The hot gases exhausting from the combustor outlet typically flow below 0.2 mach. The hot gases accelerate slightly as they travel within the transition duct, but most of the acceleration occurs as the hot gases flow through the guide vanes, where the hot gases are accelerated to approximately 0.7-0.9 mach.
Cooling requirements for the transition duct are influenced by the speed of the hot gases flowing through the transition duct. Since the speed of the hot gases flowing through conventional transition ducts remains reasonably constant along the length of the transition duct, conventional transition duct cooling arrangements have been designed to remove heat at relatively constant rates along the length of the transition duct.
In contrast to the conventional combustion arrangements, an emerging can-annular combustion arrangement reorients the combustors and directs the hot gases along a straight flow path toward the turbine inlet annulus. The associated transition duct technology uses the transition duct itself to accelerate the hot gases, thereby eliminating the guide vanes conventionally placed between the transition duct and the turbine rotor inlet. Accelerating the combustion gases within the transition duct increases the amount of heat transferred to the transition duct in those regions where the hot gases flow faster. Consequently, there remains room in the art for improved cooling arrangements.